Excimer Lamp and Ultraviolet Irradiation Device

Abstract

To provide an excimer lamp or an ultraviolet light irradiation device that reduces light in a wavelength band that is feared to have an adverse effect on a human body.SOLUTION: In an excimer lamp, a luminescent gas including a krypton gas and a chlorine gas is enclosed in a sealed body made of fused silica glass having an absorption band between wavelengths of 240 nm and 260 nm. An ultraviolet light irradiation device includes in the sealed body, an excimer lamp containing a krypton gas and a chlorine gas as luminous gases, and a housing containing the excimer lamp and an extraction portion for extracting the ultraviolet light emitted from the excimer lamp, and fused silica glass disposed in the extraction portion and having an absorption band between wavelengths of 240 nm and 260 nm.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] This invention relates to an excimer lamp and an ultraviolet irradiation device.

Background Art

[0002] DNA is known to exhibit the highest absorption characteristics near a wavelength of 260 nm. Also, a low-pressure mercury lamp exhibits a high emission spectrum near a wavelength of 254 nm. For this reason, conventionally, a technique of performing sterilization by irradiating ultraviolet light from a low-pressure mercury lamp has been widely used.

[0003] However, light near a wavelength of 254 nm may have an adverse effect when irradiated on the human body. In recent years, it has been found that ultraviolet light with a wavelength of 235 nm or less has significantly reduced harm to the human body, and techniques for performing sterilization and virus inactivation using ultraviolet light with a wavelength of 235 nm or less have become known.

[0004] As a light source that emits light in a wavelength band of 235 nm or less, a KrCl excimer lamp is known (see Patent Document 1). The KrCl excimer lamp encloses krypton gas and chlorine gas as emission gases in a casing. Then, by applying energy to the emission gas, krypton and chlorine form an excited dimer (KrCl * ), and when transitioning to the ground state, emit ultraviolet light with a main peak wavelength of 222 nm.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] FIG. 1 shows the emission spectrum of a KrCl excimer lamp. The KrCl excimer lamp has a slight light output even in a wavelength band of 240 nm or more where there is concern about adverse effects on the human body. In order to use the KrCl excimer lamp more safely, it is desirable to reduce the light in such a wavelength band of 240 nm or more.

[0007] An object of the present invention is to provide an excimer lamp or an ultraviolet irradiation device that reduces light in a wavelength band where there is concern about adverse effects on the human body.

Means for Solving the Problems

[0008] As described above, the KrCl excimer lamp emits ultraviolet light with a very short wavelength having a main peak wavelength of 222 nm. Therefore, synthetic quartz glass, which can obtain a high transmittance even for short-wavelength ultraviolet light, has been used for members (for example, the enclosure of the lamp) through which the radiation light of the KrCl excimer lamp passes. Synthetic quartz glass has not only the advantage of high light transmittance but also the advantages of excellent electrical insulation and chemical stability.

[0009] On the other hand, fused quartz glass has generally lower transmittance of short-wavelength ultraviolet light and is inferior in electrical insulation and chemical stability compared to synthetic quartz glass, and has thus been considered unsuitable as an optical member used in a KrCl excimer lamp and its irradiation device. However, as a result of the intensive research by the present inventor, it has been found that a part of the fused quartz glass has a characteristic that synthetic quartz glass does not have, that is, it has an absorption band that reduces light in the wavelength band of 240 nm to 260 nm. And an excimer lamp that makes use of the found characteristic has been devised. Although the details will be described later, it is considered that oxygen defects contained in the fused quartz glass are involved in the manifestation of this characteristic.

[0010] An excimer lamp according to an embodiment is a KrCl excimer lamp in which a light-emitting gas containing krypton gas and chlorine gas is enclosed in an envelope made of fused silica glass having an absorption band between wavelengths of 240 nm and 260 nm. Although details will be described later, the "fused silica glass having an absorption band" has two contact points where the transmittance curve and the double tangent of the transmittance curve are in contact in the transmittance spectrum of the fused silica glass, and in the wavelength band between these two contact points, the transmittance of the transmittance curve is lower than the transmittance of the double tangent. Also, when at least a part of the "wavelength band between the two contact points" overlaps with the wavelength range of 240 nm or more and 260 nm or less, the fused silica glass "has an absorption band between wavelengths of 240 nm and 260 nm". By configuring the envelope with fused silica glass having an absorption band between wavelengths of 240 nm and 260 nm, light in the wavelength band of 240 nm to 260 nm radiated from the KrCl excimer lamp is reduced by the envelope. As a result, sterilization and virus inactivation can be performed using ultraviolet light having a wavelength of less than 235 nm while minimizing adverse effects on the human body.

[0011] Performing sterilization and virus inactivation with an excimer lamp corresponds to Goal 3 of the United Nations-led Sustainable Development Goals (SDGs), "Ensure healthy lives and promote well-being for all people of all ages", and also greatly contributes to Target 3.3, "By 2030, end the epidemics of AIDS, tuberculosis, malaria and neglected tropical diseases and combat hepatitis, waterborne diseases and other infectious diseases".

[0012] The minimum value of the transmittance of the fused silica glass may be between 235 nm and 250 nm. Thereby, the reduction effect of light in a particularly restricted wavelength band radiated from the KrCl excimer lamp is expanded.

[0013] When the light intensity of light having a wavelength of 350 nm passing through the fused silica glass is set to 1, the light intensity at the minimum value of the transmittance of the fused silica glass may be 0.95 or less.

[0014] The OH group concentration of the fused silica glass may be 50 wt.ppm or less. Although heat may be applied to the fused silica glass in the process of forming the enclosure, etc., if the fused silica glass contains a large amount of OH groups, as the fused silica glass is heated, the OH groups may repair oxygen defects and reduce the oxygen defects. Since oxygen defects selectively absorb light in the wavelength band of 240 to 260 nm, the reduction of oxygen defects hinders the absorption of light in the wavelength band of 240 to 260 nm. Therefore, by restricting the OH groups to 50 wt.ppm or less, it becomes difficult to repair oxygen defects even when the fused silica glass is heated.

[0015] At least one of the following may be satisfied: the Ti concentration contained in the fused silica glass is 5 wt.ppm or less, the Fe concentration contained in the fused silica glass is 3 wt.ppm or less, and the Mn concentration contained in the fused silica glass is 3 wt.ppm or less. Ti, Fe, and Mn deteriorate the transmittance of the fused silica glass for ultraviolet light with a main peak wavelength of 222 nm emitted from a KrCl excimer lamp. By restricting at least one of the concentrations of Ti, Fe, and Mn to the above predetermined value or less, it becomes easier to maintain the transmittance of the fused silica glass for ultraviolet light with a main peak wavelength of 222 nm at a high level.

[0016] The fused silica glass may be arranged not only in the enclosure of the excimer lamp but also in the extraction part of the ultraviolet light emitted from the excimer lamp in the housing that houses the excimer lamp in the ultraviolet light irradiation device. For example, an ultraviolet light irradiation device according to an embodiment includes an excimer lamp having the above-described characteristics, and a housing that houses the excimer lamp and has an extraction part for extracting ultraviolet light emitted from the excimer lamp, and the fused silica glass that is arranged in the extraction part and has an absorption band between 240 nm and 260 nm in wavelength.

[0017] The ultraviolet light irradiation device of one embodiment includes, in an enclosure that may not be made of fused quartz glass having an absorption band between wavelengths of 240 nm and 260 nm, an excimer lamp containing krypton gas and chlorine gas as a luminescent gas, and a housing having a take-out portion that houses the excimer lamp and takes out ultraviolet light radiated from the excimer lamp, and a fused quartz glass that is disposed in the take-out portion and has an absorption band between wavelengths of 240 nm and 260 nm.

[0018] And for the fused quartz glass disposed in the take-out portion, the same additional configuration as the fused quartz glass constituting the enclosure may be applied.

Effect of the Invention

[0019] Thereby, an excimer lamp or an ultraviolet light irradiation device that reduces light in a wavelength band that raises concerns about adverse effects on the human body can be provided.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6A

Figure 6B

Figure 7

Figure 8

Figure 9

Best Mode for Carrying Out the Invention

[0021] An embodiment of an ultraviolet light irradiation device will be described with reference to the drawings. It should be noted that the following drawings are schematically illustrated, and the dimensional ratios on the drawings do not necessarily match the actual dimensional ratios, and the dimensional ratios do not necessarily match between the drawings.

[0022] In the following, each drawing will be described while appropriately referring to the XYZ coordinate system. In the XYZ coordinate system, the direction in which the light ray on the optical axis of the radiated ultraviolet light travels is defined as the +X direction, and the plane orthogonal to the X direction is defined as the YZ plane. In this specification, when expressing a direction and distinguishing between positive and negative directions, it is described with positive and negative signs, such as "+X direction" and "-X direction". When expressing a direction without distinguishing between positive and negative directions, it is simply described as "X direction". That is, in this specification, when simply described as "X direction", both the "+X direction" and the "-X direction" are included. The same applies to the Y direction and the Z direction.

[0023] <First Embodiment> [Overview of Ultraviolet Light Irradiation Device] With reference to FIGS. 2, 3 and 4, an overview of an embodiment of the ultraviolet light irradiation device will be described. FIGS. 2 and 3 are perspective views of the ultraviolet light irradiation device. FIG. 4 is a cross-sectional view taken along the C1 plane of FIG. 2.

[0024] The ultraviolet light irradiation device 10 of the present embodiment includes an excimer lamp 3 that emits ultraviolet light, a housing 2 that houses the excimer lamp 3, and an extraction unit 4 for extracting the ultraviolet light radiated from the excimer lamp 3 in the +X direction outside the housing 2. As shown in FIG. 4, an ultraviolet light transmissive material 11 that transmits ultraviolet light is disposed in the extraction unit 4 so as to be fitted therein. The ultraviolet light transmissive material 11 partitions the outside and the inside of the housing 2. The ultraviolet light transmissive material 11 may be made of synthetic quartz glass.

[0025] In FIGS. 2, 3, and 4, the optical axis of the light emitted from the extraction unit 4 is labeled "L1". An arrow indicating the traveling direction of the light beam emitted on the optical axis L1 is added. The tube axis direction of each of the three excimer lamps 3 is along the Y direction, and the direction in which the excimer lamps 3 are arranged is along the Z direction.

[0026] In this embodiment, the housing 2 is composed of a first frame 2a having an opening that functions as an extraction unit 4 at the center and a second frame 2b having no opening. The second frame 2b and the first frame 2a are fitted together to form an internal space surrounded by the housing 2. In this internal space, an excimer lamp 3 and two electrode blocks (9a, 9b) for supplying power to the excimer lamp 3 are arranged (see FIG. 4). The frame constituting the housing 2 may be composed of three or more.

[0027] The two electrode blocks (9a, 9b) are fixed to the inner surface of the second frame 2b (see FIG. 3 or FIG. 4). Two connection terminals (8a, 8b) are provided on the outer surface of the second frame 2b (see FIG. 3). The two connection terminals (8a, 8b) are respectively in conduction with the electrode blocks (9a, 9b) with the second frame 2b interposed therebetween. Feeding lines (7a, 7b) fed from an external power source (not shown) are respectively connected to the two connection terminals (8a, 8b).

[0028] FIG. 5 is a perspective view showing only the excimer lamp 3 and the electrode blocks (9a, 9b) taken out from the ultraviolet light irradiation device. The excimer lamp 3 includes a hollow enclosure 5, and a light-emitting gas is enclosed therein. The enclosure 5 is in contact with the two electrode blocks (9a, 9b), respectively, whereby each excimer lamp 3 is supplied with power.

[0029] The light-emitting gas is a mixed gas of krypton gas and chlorine gas. When a high voltage is applied to the electrode blocks (9a, 9b), dielectric barrier discharge occurs inside the enclosure 5, and excited dimers of krypton and chlorine (KrCl *) is formed. When this excited dimer returns to the ground state, it emits ultraviolet light with a main peak wavelength of 222 nm. The emitted ultraviolet light passes through the enclosure 5 and is radiated outside the excimer lamp 3. Note that the excimer lamp 3 shown in FIGS. 2 to 5 is merely an example of an embodiment, and matters other than that krypton gas and chlorine gas are enclosed in the enclosure 5, such as the shape of the enclosure 5, the arrangement or shape of the electrodes, etc., are not particularly limited.

[0030] [Enclosure] In this embodiment, fused silica glass is used for the enclosure 5 that transmits ultraviolet light. The reason will be described with reference to FIGS. 6A and 6B. FIGS. 6A and 6B respectively show the transmission spectra of quartz glass. In FIG. 6A, the transmittance curve S1 shows an example of the transmission spectrum of fused silica glass. In FIG. 6B, the transmittance curve S2 shows an example of the transmission spectrum of fused silica glass having an absorption band, the transmittance curve S3 shows an example of the transmission spectrum of fused silica glass having no absorption band, and the transmittance curve S4 shows an example of the transmission spectrum of synthetic quartz glass. The vertical axes in FIGS. 6A and 6B respectively represent the relative transmittance at each wavelength when the transmittance of quartz glass transmitting light of 350 nm is set to 100%.

[0031] Referring to the transmittance curve S1 in FIG. 6A, the change in the transmittance of the fused silica glass having the transmittance curve S1 will be described from the larger wavelength to the smaller wavelength. As the wavelength goes from 350 nm to 262 nm, the transmittance gradually decreases. The transmittance starts to rapidly decrease from 262 nm, and the decrease in transmittance continues until 242 nm. 242 nm is the minimum value. As the wavelength goes from 242 nm to 226 nm, the transmittance increases. 226 nm is the maximum value. When the wavelength becomes smaller than 226 nm, the transmittance starts to decrease, and when the wavelength is less than 215 nm, the transmittance is less than 80%.

[0032] When drawing a tangent to the transmittance curve S1, a double tangent T1 that contacts the transmittance curve S1 at two points (Cp1, Cp2) can be drawn. The wavelength band A1 between the contact points (Cp1, Cp2) of the transmittance curve S1 and the double tangent T1 is the absorption band of the fused silica glass having the transmittance curve S1. The absorption band A1 of the fused silica glass shown in Fig. 6A is 226 nm to 262 nm.

[0033] Since the absorption band A1 overlaps with the wavelength range of 240 nm or more and 260 nm or less, the fused silica glass having this absorption band A1 is "fused silica glass having an absorption band between wavelengths of 240 nm and 260 nm". By transmitting the radiation light from a KrCl excimer lamp through this fused silica glass, it is possible to obtain the effect of reducing the light in the wavelength band of 240 nm to 260 nm, which may have an adverse effect on the human body. And the main peak wavelength of 222 nm is close to the maximum value of the transmittance curve S1 and is not between wavelengths of 240 nm and 260 nm, so it transmits more light than the wavelength to be restricted.

[0034] In addition, it is known that ultraviolet light with a wavelength of 200 nm or less generates ozone from oxygen in the atmosphere. When the ozone concentration is high, it may have an adverse effect on the human body. Since the transmittance curve S1 has a low transmittance for ultraviolet light with a wavelength of 200 nm or less, transmitting the radiation light from a KrCl excimer lamp through this fused silica glass leads to a decrease in the probability of ozone generation. This effect cannot be obtained with the synthetic silica glass described later.

[0035] Referring to the transmittance curve S2 in Fig. 6B, similar to the transmittance curve S1, a double tangent to the transmittance curve S2 can be drawn for the transmittance curve S2, and it has two contact points with the double tangent. And the absorption band A2, which is the wavelength band between the two contact points, overlaps with the wavelength range of 240 nm or more and 260 nm or less. Therefore, the fused silica glass having this absorption band A2 is "fused silica glass having an absorption band between wavelengths of 240 nm and 260 nm".

[0036] While referring to the transmittance curve S3 in FIG. 6B, the change in the transmittance of the fused silica glass having the transmittance curve S3 will be described from the larger wavelength to the smaller wavelength. As the wavelength goes from 350 nm to 233 nm, the transmittance gradually decreases. The transmittance begins to rapidly decrease from 233 nm. The rapid decrease in transmittance continues until around 200 nm. There are no maximum and minimum values in the transmittance curve S3. When drawing a tangent to the transmittance curve S3, although a tangent having only one contact point can be drawn, a double tangent that contacts the transmittance curve S3 at two points cannot be drawn. The fused silica glass having the transmittance curve S3 does not have an absorption band.

[0037] While referring to the transmittance curve S4 in FIG. 6B, the change in the transmittance of the synthetic quartz glass having the transmittance curve S4 will be described from the larger wavelength to the smaller wavelength. As the wavelength goes from 350 nm to 200 nm, the transmittance gradually decreases. There are no maximum and minimum values in the transmittance curve S4. When drawing a tangent to the transmittance curve S4, although a tangent having only one contact point can be drawn, a double tangent that contacts the transmittance curve S4 at two points cannot be drawn. Therefore, the synthetic quartz glass having the transmittance curve S4 does not have an absorption band. The synthetic quartz glass having the transmittance curve S4 has a transmittance of 95% or more in all of the wavelength bands from 200 to 350 nm.

[0038] The maximum value of the decrease width of the transmittance appears at the minimum value of the transmittance curve. As described above, the minimum value of the transmittance curve S1 is when the wavelength is 242 nm. When the minimum value is between 240 nm and 250 nm, the light reduction effect of the absorption band A1 in the particularly desired wavelength band is enlarged. Also, one having the minimum value of the transmittance curve S1 in the wavelength band from 235 nm to 250 nm including the particularly desired wavelength band may be used. The minimum value of the transmittance curve S1 in FIG. 6A shows 92 (%). When the light intensity of the light having a wavelength of 350 nm passing through the fused silica glass is 1 (transmittance is 100%), it is preferable that the light intensity at the minimum value of the transmittance curve of the fused silica glass is 0.95 or less (transmittance is 95% or less).

[0039] In FIG. 6A, the transmittance of the absorption band A1 of the transmittance curve S1 shows a maximum decrease width d1 of 3% compared to the transmittance of the double tangent. Although it is preferable that the decrease width d1 is larger, the decrease width d1 of the transmittance of the absorption band A1 may be small. For example, the decrease width d1 of the transmittance of the absorption band A1 with respect to the transmittance of the double tangent may be 1% or more. Also, the transmittance difference between the maximum value and the minimum value may be 1% or more, preferably 2% or more, and more preferably 3% or more.

[0040] [Oxygen defect] The presence of the absorption bands (A1, A2) overlapping with the wavelength band of 240 to 260 nm described above is due to the fact that the fused silica glass contains a large amount of oxygen defects. Quartz glass is usually a structure in which regular tetrahedrons of SiO4 are irregularly bonded as units. However, in the part called an oxygen defect, SiO4 is not formed and has a defect structure in which O is not bonded to Si. And the defect structure absorbs light of a specific wavelength. The transmittance curves of fused silica glass and synthetic quartz glass with few oxygen defects do not have an absorption band. Examples of fused silica glass having oxygen defects include GE214 manufactured by MOMENTIVE and PQ871 manufactured by PACIFIC QUARTZ. In addition, fused silica glass manufactured by the electric melting method tends to have desired oxygen defects remaining and is easily applicable as the fused silica glass of the present invention.

[0041] Oxygen defects include multiple types due to differences in defect structures, such as SLPC defects, NBOHC defects, or ODC defects. Each type of defect structure has a different absorption band peak, and as a result, absorbs light of a specific wavelength. For example, SLPC defects have an energy absorption band peak of 5.15 eV and absorb light with a wavelength of 241 nm. NBOHC defects have an energy absorption band peak of 4.8 eV and absorb light with a wavelength of 258 nm. ODC defects have an energy absorption band peak of 5.02 eV and absorb light with a wavelength of 247 nm. These various oxygen defects selectively absorb light in the wavelength band of 240 - 260 nm. The more oxygen defects there are, the greater the absorption of light of the specific wavelength. The extent of oxygen defects present in fused silica glass can be estimated by analyzing the transmittance spectrum or absorption spectrum of the fused silica glass. In FIG. 6A, the absorption band A1 of the transmittance curve S1 is 226 - 262 nm, but by adjusting the defect amount or the thickness of the glass, the wavelength width of the absorption band can be expanded, reduced, or shifted, or the absorption amount (transmittance) can be increased or decreased.

[0042] A part of the fused silica glass contains OH groups. When the fused silica glass is heated and activated, the OH groups in the fused silica glass function as a source of oxygen atoms for repairing oxygen defects. In this embodiment, when the oxygen defects decrease due to such repair of oxygen defects, it becomes difficult to selectively absorb light in the wavelength band of 240 - 260 nm. Therefore, the OH group concentration in the fused silica glass is preferably below a specified value.

[0043] The OH group concentration in the fused silica glass is preferably 50 wt.ppm or less, more preferably 30 wt.ppm or less, and even more preferably 20 wt.ppm or less. Fused silica glass with a low OH group concentration includes relatively more electrically melted quartz produced by the electric melting method. The fused silica glass is heated in the process of processing the fused silica glass, for example, in the process of processing the fused silica glass into the shape of the enclosure 5 of the excimer lamp 3. Also, by intentionally subjecting the fused silica glass to heat treatment, oxygen defects can be repaired to bring the amount of oxygen defects closer to a desired value.

[0044] The concentration of OH groups contained in fused silica can be calculated from the infrared absorption spectrum. The calculation procedure for the OH group concentration will be described. Infrared rays are irradiated onto fused silica with a thickness t [mm] to be measured, and the infrared rays transmitted through the fused silica are measured with an infrared spectrophotometer. From this, an infrared absorption spectrum is obtained. Then, regarding the infrared absorption band near a wavelength of 2.73 μm caused by OH groups (hydroxyl groups) in the fused silica in the infrared absorption spectrum, the transmittance (Tb [%]) at the wavelength of the infrared absorption peak in the absorption band and the transmittance (Ta [%]) at a wavelength not affected by infrared absorption (here, the transmittance [%] at a wavelength of 2.60 μm) are read. The OH group concentration (C [wt.ppm]) in the fused silica is calculated based on the following formula (1). OH group concentration (C) = (1 / t) × (Log 10 (Ta / Tb)) × 997 …(1)

[0045] The impurities contained in the fused silica reduce the transmittance of ultraviolet light with a main peak wavelength of 222 nm emitted from a KrCl excimer lamp. Among the impurities, in particular, Ti, Fe, or Mn is likely to be contained in the fused silica as an impurity and is likely to cause a reduction in transmittance. Therefore, it is preferable that the concentration of at least any one of Ti, Fe, and Mn contained in the fused silica is below a specified value.

[0046] For example, the concentration of Ti is preferably 5 wt.ppm or less, and more preferably 3 wt.ppm or less. This makes it easier to maintain the transmittance of ultraviolet light with a main peak wavelength of 222 nm at a high level. For example, the concentration of Fe contained in the fused silica is preferably 3 wt.ppm or less, and more preferably 1.5 wt.ppm or less. This makes it easier to maintain the transmittance of ultraviolet light with a main peak wavelength of 222 nm at a high level. For example, the concentration of Mn contained in fused silica glass is preferably 3 wt.ppm or less, more preferably 1 wt.ppm or less. This makes it easier to maintain a high transmittance of ultraviolet light with a main peak wavelength of 222 nm. The impurity concentration in fused silica glass such as Ti, Fe, or Mn can be measured using inductively coupled plasma mass spectrometry (ICP-MS).

[0047] The absorption coefficient of fused silica glass for ultraviolet light with a wavelength of 240 nm is, for example, preferably 0.05 to 5 / mm, more preferably 1 to 5 / mm, and even more preferably 2 to 5 / mm.

[0048] The thickness of the enclosure is preferably 5 mm or less, more preferably 2 mm or less. This can suppress a decrease in the transmittance of ultraviolet light with a main peak wavelength of 222 nm, and a large irradiance can be obtained even when using fused silica glass. The thickness of the enclosure is preferably 0.5 mm or more, more preferably 1 mm or more. The thicker the enclosure, the greater the light reduction effect in the wavelength band of 240 to 260 nm.

[0049] Referring to FIG. 7, a modified example of the ultraviolet light irradiation device will be described. The ultraviolet light irradiation device 15 includes an optical filter 6 that transmits ultraviolet light belonging to the wavelength band of 190 nm to 235 nm and inhibits the transmission of ultraviolet light in the wavelength band of 240 nm to 280 nm. For example, when the emitted light from the light source is incident on the optical filter at an incident angle of 0 degrees, with respect to the light intensity of the peak wavelength in the wavelength band of 190 nm to 235 nm among the ultraviolet light emitted from the light source, the light intensity of the ultraviolet light in the wavelength band of 240 nm to 280 nm after passing through the optical filter is attenuated to 3% or less, and further 1% or less. An optical filter can be adopted. In addition to using fused quartz glass for the envelope 5 of the excimer lamp 3, by arranging the optical filter 6 at the extraction part 4, the ultraviolet light in the range of 240 nm to 280 nm can be further reduced, and the safety of the ultraviolet light irradiation device 15 to the human body can be further improved. Furthermore, the optical filter 6 is preferably an optical filter that inhibits transmission in the wavelength band of 280 to 320 nm in addition to the above-described wavelength band, because the safety is further enhanced.

[0050] The arrangement location and form of the optical filter 6 are not limited. As shown in FIG. 7, in addition to the optical filter 6 being formed separately from the excimer lamp 3, the optical filter 6 may be formed in contact with the excimer lamp 3 (as a specific example, the optical filter 6 may be laminated on the surface of the envelope 5).

[0051] The optical filter 6 is formed, for example, by forming a dielectric multilayer film in which dielectric films having different refractive indexes are alternately laminated on a substrate made of quartz glass. As the dielectric multilayer film, for example, there are those in which HfO2 layers and SiO2 layers are alternately laminated, and those in which SiO2 layers and Al2O3 layers are alternately laminated. The dielectric multilayer film in which HfO2 layers and SiO2 layers are alternately laminated can reduce the number of layers for obtaining the same wavelength selection characteristics compared to the dielectric multilayer film in which SiO2 layers and Al2O3 layers are alternately laminated, and thus can increase the transmittance of the selected ultraviolet light.

[0052] <Second Embodiment> Referring to FIG. 8, a second embodiment of the ultraviolet light irradiation device will be described. Regarding matters other than those shown below, they are the same as in the first embodiment. In the ultraviolet light irradiation device 20, a fused silica glass 12 having an absorption band between wavelengths of 240 nm and 260 nm is disposed in the extraction portion 4. Thereby, the amount of light in the wavelength band of 240 nm to 260 nm radiated from the excimer lamp 3 to the ultraviolet light irradiation device 20 can be reduced.

[0053] Since the fused silica glass 12 having an absorption band between wavelengths of 240 nm and 260 nm is disposed in the extraction portion 4 of the ultraviolet light irradiation device 20, in the ultraviolet light irradiation device 20, the enclosure 5 of the excimer lamp 3 does not need to be made of a fused silica glass having an absorption band between wavelengths of 240 nm and 260 nm. That is, the enclosure 5 may be made of a fused silica glass or a synthetic silica glass having no absorption band. When the enclosure 5 of the excimer lamp 3 is made of a fused silica glass having an absorption band between wavelengths of 240 nm and 260 nm, the light in the wavelength band of 240 nm to 260 nm can be further reduced.

[0054] FIG. 9 shows a further modification of the second embodiment. The ultraviolet light irradiation device 25 has an optical filter 13 in which a dielectric multilayer film is laminated on a fused silica glass serving as a base material and having an absorption band between wavelengths of 240 nm and 260 nm in the extraction portion 4. The optical filter 13 can obtain both the effect of reducing the light in the wavelength band of 240 nm to 260 nm by the fused silica glass having an absorption band between wavelengths of 240 nm and 260 nm and the effect of reducing the light in the wavelength band of 240 nm to 260 nm by the dielectric multilayer film.

Description of Reference Numerals

[0055] 2: Housing 2a: First frame 2b: Second frame 3: Excimer lamp 4: Extraction portion 5: Enclosure 6: Optical filter 10, 15, 20, 25: Ultraviolet light irradiation device 11: Ultraviolet light transmitting material 12: Fused silica glass 13: Optical filter A1: Absorption band L1: Optical axis

Claims

1. In an enclosure made of fused silica glass having an absorption band between 240 nm and 260 nm in wavelength, a luminescent gas containing krypton gas and chlorine gas is enclosed. The fused silica glass has a transmittance at a wavelength of 222 nm higher than the transmittance corresponding to the minimum value of the absorption band. An excimer lamp, characterized in that when the light intensity of light having a wavelength of 350 nm passing through the fused silica glass is taken as 1, the light intensity at the minimum value of the transmittance of the fused silica glass is 0.95 or less.

2. The excimer lamp according to claim 1, characterized in that the minimum value of the transmittance of the fused silica glass is between 235 nm and 250 nm.

3. The excimer lamp according to claim 1 or 2, characterized in that the OH group concentration of the fused silica glass is 50 wt.ppm or less.

4. The Ti concentration contained in the fused silica glass is 5 wt.ppm or less. The Fe concentration contained in the fused silica glass is 3 wt.ppm or less. And the Mn concentration contained in the fused silica glass is 3 wt.ppm or less. The excimer lamp according to claim 1 or 2, characterized by satisfying at least any one of the above.

5. An excimer lamp according to any one of claims 1 to 4, A housing that houses the excimer lamp and has an extraction part for extracting ultraviolet light radiated from the excimer lamp, An ultraviolet light irradiation device, characterized by comprising a fused silica glass that is disposed in the extraction part and has an absorption band between 240 nm and 260 nm in wavelength.

6. In an enclosure, an excimer lamp containing krypton gas and chlorine gas as a luminescent gas, A housing that houses the excimer lamp and has an extraction part for extracting ultraviolet light radiated from the excimer lamp, And a fused silica glass that is disposed in the extraction part and has an absorption band between 240 nm and 260 nm in wavelength. The fused silica glass has a transmittance at a wavelength of 222 nm higher than the transmittance corresponding to the minimum value of the absorption band. An ultraviolet light irradiation device, characterized in that when the light intensity of light having a wavelength of 350 nm passing through the fused silica glass is taken as 1, the light intensity at the minimum value of the transmittance of the fused silica glass is 0.95 or less.

7. The ultraviolet light irradiation device according to claim 6, wherein the minimum value of the transmittance of the fused silica glass is in the range of 240 nm or more and 250 nm or less.

8. The ultraviolet light irradiation device according to claim 6 or 7, wherein the OH group concentration of the fused silica glass is 50 wt.ppm or less.

9. The Ti concentration contained in the fused silica glass is 5 wt.ppm or less, the Fe concentration contained in the fused silica glass is 3 wt.ppm or less, and the Mn concentration contained in the fused silica glass is 3 wt.ppm or less, and the ultraviolet light irradiation device according to claim 6 or 7 satisfies at least one of the above.

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